Heat sink

ABSTRACT

A heat sink comprising (a) a plate-shaped heat pipe including an upper plate member and a lower plate member to form a hermetically sealed cavity, and a working fluid enclosed therein, and (b) at least one heat radiating fin integrally formed with the upper plate member on an outer surface of the upper plate member.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a heat sink which may be adaptedfor use in a heat dissipation of an electronic equipment and the likehaving a heat generating part which needs to be cooled.

[0003] 2. Related Art

[0004] In recent years, an electronic element such as a semiconductordevice and the like to be mounted on various electronic or electricequipment such as a personal computer and the like has been denselyintegrated, the output thereof has become large, and an amount of heatgenerated therefrom has increased. It has become an important technicalproblem which is to be solved to cool such an electronic equipmenthaving heat generating parts, and the improvement in such coolingtechniques attracts people's attention. As a method for preventing theheat generating electric element (hereinafter referred to as “heatgenerating part”) from being overheated, there is known a method oflowering the temperature of the air inside the body encasing theelectronic equipment by a fan attached thereto so as to discharge theair and cool the heat generating part, or a method of cooling the heatgenerating part by a cooling member which is attaching to the heatgenerating part and removes heat from the heat generating part.

[0005] The cooling member which is attached to the heat generating partis generally called as a heat sink, and is often used in the form of aplate member made of a material being excellent in thermal conductivitysuch as copper, aluminum and the like. In order to efficiently dischargethe heat which is transferred from the heat generating part to the platemember as the cooling member, heat radiating fins are often integrallyformed with the plate member. In addition, there is also an embodimentin which a heat pipe is attached to the above-mentioned plate member totransfer the heat from the plate member to a prescribed place, andfurthermore, heat radiating fins are attached to the portion in theprescribed place which is separated from the heat generating part, thustransferring the heat and then dissipating therefrom the transferredheat.

[0006] In addition, in order to improve the uniformity in heatabsorption of the plate member, a heat pipe is sometimes attached to orburied in the plate member. Improvement of the uniformity in heatabsorption of the plate member makes it possible to more efficientlyabsorb the heat generated by the heat generating part.

[0007] A heat pipe which has been used up to now is briefly described.The heat pipe includes a container having a hermetically sealed cavityand a working fluid enclosed in the container. The heat pipe hasgenerally a heat absorption (i.e., evaporator) side and a heat radiation(i.e., condenser) side. The heat pipe has a function of moving heat fromthe evaporator side to the condenser side by means of a phasetransformation of the working fluid enclosed in the cavity from agaseous phase to a liquid phase or from a liquid phase to a gaseousphase, and the movement of thus phase-transformed working fluid insidethe cavity.

[0008] More specifically, in the heat absorption side of the heat pipe,the working fluid enclosed inside the hermetically sealed cavity isevaporated by the heat thermally transferred from the heat generatingpart through the material of the container forming the heat pipe, andthe vapor of the working fluid which has been transformed in phasepasses through the inside of the cavity and moves to the condenser sideof the heat pipe. In the condenser side, the vapor of the working fluidis cooled and returns to the liquid phase. The working fluid which hasreturned to the liquid phase flows back to the evaporator side. Asdescribed above, movement of heat is performed by a phase transformationand movement of the phase-transformed working fluid. In order to make iteasy to transform the working fluid in phase, the cavity is degassed andhermetically sealed.

[0009] Since a cooling structure (i.e., cooling device) in which thecooling member is attached to the heat generating part, and heatradiating fins are further attached to the cooling member canefficiently cool the heat generating part, although it is comparativelysmall in size, the cooling structure is expected to be an effectivecooling means.

[0010] In recent years, a marked tendency may be seen to make small insize various kinds of electronic equipment having semiconductor deviceswhich need to be cooled. Accordingly, there is a trend to restrict thespace in which the cooling structure used for cooling the part is to beinstalled.

[0011] In order to realize a small-sized (space-saving) coolingstructure, it is necessary to realize a more efficient heat dissipatingmeans. Moreover, since an amount of heat generated by an electronicequipment has increased, it is required to develop a cooling structurecapable of effectively dissipating a large amount of heat. Such acooling structure has not yet been proposed.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a coolingstructure which is compact, however, simultaneously can realize anexcellent cooling performance, and furthermore, can dissipate a largeamount of heat.

[0013] The present invention has been made in order to attain theabove-mentioned object. According to the present invention, there isproposed a first embodiment of a heat sink comprising;

[0014] (a) a plate-shaped heat pipe including an upper plate member anda lower plate member to form a hermetically sealed cavity, and a workingfluid enclosed therein, and

[0015] (b) at least one heat radiating fin integrally formed with saidupper plate member on an outer surface of said upper plate member.

[0016] According to the present invention, there is proposed a secondembodiment of a heat sink, wherein a heat transferring metal column forjoining said upper plate member and said lower plate member with eachother in said cavity of said heat sink is integrally formed with saidlower plate member on a portion corresponding to a heat absorbingportion of said plate-shaped heat pipe.

[0017] According to the present invention, there is proposed a thirdembodiment of a heat sink, wherein a total area of side wall portion ofsaid heat transferring metal column is larger than a sectional area ofsaid heat transferring metal column.

[0018] According to the present invention, there is proposed a fourthembodiment of a heat sink, wherein at least one pressure resisting metalpart is integrally formed with said upper plate member and/or said lowerplate member in said cavity of said heat sink.

[0019] According to the present invention, there is proposed a fifthembodiment of a heat sink, wherein each of said heat radiating fin andsaid pressure resisting metal part comprises at least two portions or asingle portion, and said at least two portions are intermittentlyarranged in a radial manner, whereas said single portion is continuouslyarranged in a radial manner.

[0020] According to the present invention, there is proposed a sixthembodiment of a heat sink, wherein each of said heat radiating fin andsaid pressure resisting metal part comprises at least two portions or asingle portion, and said at least two portions are intermittentlyarranged in a shape of a swirl, whereas said single portion iscontinuously arranged in a shape of a swirl.

[0021] According to the present invention, there is proposed a seventhembodiment of a heat sink, wherein a wick is disposed in said cavity ofsaid heat pipe.

[0022] According to the present invention, there is proposed a eighthembodiment of a heat sink, wherein an electrically driven fan isdisposed at a location facing said heat radiating fin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a schematic sectional view for explaining an example ofa heat sink of the present invention.

[0024]FIG. 2 is a schematic perspective view for explaining an exampleof an upper plate member of a heat sink of the present invention.

[0025]FIG. 3 is a schematic perspective view., partially in crosssection, for explaining another example of a heat sink of the presentinvention.

[0026]FIG. 4 is a schematic sectional view for explaining anotherexample of a heat sink of the present invention.

[0027]FIG. 5 is a schematic view for explaining another example of anupper plate member of a heat sink of the present invention.

[0028]FIG. 6 is a schematic view for explaining another example of anupper plate member of a heat sink of the present invention.

[0029]FIG. 7 is a schematic sectional view for explaining anotherexample of a heat sink of the present invention.

[0030]FIG. 8 is a schematic view for explaining evaporation areas incomparison with each other in case that there is a heat transferringmetal column and in case that there is no heat transferring metalcolumn.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031]FIG. 1 is a schematic sectional view for explaining an embodimentof a heat sink of the present invention.

[0032] A heat generating part 40 which is an electronic equipment to becooled is set on an outer surface of a lower plate member 20 of a heatsink 1 of the present invention. The heat sink 1 includes a heat pipestructure having a hermetically sealed cavity 3 therein. As shown inFIG. 1, the cavity 3 of the heat pipe is formed by joining the lowerplate member 20 to an upper plate member 10 which is integrally formedin one body with a container part 100 and a heat radiating fin part 101(namely, formed as a unit by means of casting or the like instead ofjoining the respective portions to one another). The upper plate member10 and the lower plate member 20 are joined to each other by means of ajoining method of brazing, welding, soldering or the like. A workingfluid is enclosed in the cavity 3. Illustration of a working fluid isomitted. In FIG. 1, the reference numeral 41 represents a lead and thereference numeral 42 represents a printed wiring board.

[0033] The heat generated from the heat generating part 40 istransferred through the lower plate member 20 to the working fluidenclosed in the cavity of the heat pipe. The heat thus transferred tothe working fluid spreads out all over the heat sink uniformly in heattransfer due to a fact that the heat sink of the present inventionincludes the heat pipe structure, as described above. The heat isfurther transferred to the heat radiating fins 101 and discharged to theoutside in the air. In such a way, the heat generated by the heatgenerating part 40 is quickly discharged to the outside so as to coolthe heat generating part 40.

[0034] The upper plate member 10 which is one of the components formingthe heat sink 1 of the present invention comprises a container portion100 and a heat radiating fin portion 101. Since the container portion100 and the heat radiating fin portion 101 are integrally formed as aunit, a thermal resistance between those portions is low. Accordingly,the heat transferred through the cavity 3 is quickly transferred to theheat radiating fin portion 101. As a result, an excellent coolingperformance may be realized. It is preferable to apply such metalmaterial as an aluminum or copper being excellent in thermalconductivity as a material for the upper plate member.

[0035] Furthermore, a heat sink of the present invention whose upperplate member and fin are integrally formed as a unit is less expensivein fabricating cost in comparison with a heat sink assembled by joininga separate heat generating fin part to a plate-shaped heat pipe. Theupper plate member 10 may be less expensively manufactured by means of acasting or forging method. In the present invention, a heat sink may bemanufactured by forming a plate-shaped heat pipe, and then joining thusformed plate-shaped heat pipe with a heat generating fin part (namely,the respective components may be joined to one another).

[0036]FIG. 2 is a schematic perspective view showing an embodiment of anupper plate member which is a component of a heat sink of the presentinvention. FIG. 2 shows the upper plate member in an upside-down statein order to show more apparently its structure. The upper plate member11 shown in FIG. 2 is obtained by integrally forming as a unit acontainer portion 110 and a heat radiating fin portion 111 andadditionally a pressure resisting metal column 112. The pressureresisting metal column 112 is arranged inside a cavity of a heat pipe.The pressure resisting metal column 112 is also joined to a lower platemember (not shown) at the time of forming a heat sink by joining thelower plate member to this upper plate member 11. By forming thepressure resisting metal column 112 in such a way, even if the innerpressure of the cavity rises with the operation (evaporation) of aworking fluid, the heat sink may not distort in shape, thus increasingthe strength of the heat sink.

[0037]FIG. 3 shows another embodiment of a heat sink of the presentinvention.

[0038]FIG. 3 shows in a perspective view a section of a heat sink inwhich a heat transferring metal column 123 is disposed. The heattransferring metal column 123 is disposed on a portion (namely, a heatabsorbing portion) in the cavity corresponding to a heat generating partwhich is set on the outer surface of the lower plate member. In thisexample, the heat transferring metal column 123 is integrally formed asa unit with the upper plate member 12 together with a container portion120, a heat radiating fin portion 121 and a pressure resisting metalcolumn 122. Reference numeral 30 in FIG. 3 represents a cavity.

[0039] As shown in FIG. 3, the heat transferring metal column 123 isprovided in the cavity at the inner surface of the lower plate member(i.e., the heat absorbing part), on the outer surface of which the heatgenerating part 40 is to be set. Since the heat generating part 40 isattached to the heat transferring metal column 123 through the lowerplate member, the heat generated from the heat generating part 40 istransferred to the heat transferring metal column, and then transferredthrough each side wall of the heat transferring metal column 123 to theworking fluid, thus enabling to enlarge the evaporating area of the heatpipe. As a result, the heat transfer efficiency is remarkably improved.

[0040]FIG. 8 shows the evaporating areas in comparison with each otherin case that no heat transferring metal column is disposed and in casethat the heat transferring metal column is disposed. In FIG. 8(a), sinceno heat transferring metal column is provided, the evaporating area inthe heat pipe is restricted to only a portion being in contact with theupper face of the heat generating part (the portion is shown by slantlines). On the other hand, as shown in FIG. 8(b), in case that a heattransferring metal column is provided, since the heat generating part 8is in contact with the heat transferring metal column 91, all the fourside walls (which are shown by slant lines) of the heat transferringmetal column become the evaporating area.

[0041] In the example shown in FIG. 8(b), since the heat transferringmetal column is integrally formed as a unit with the (not shown) upperplate member, the heat transferring metal column may be provided in suchmanner that the total areas of the four side walls becomes larger thanthe sectional area of the heat transferring metal column. Furthermore,since the heat generated from the heat generating part may betransferred through the heat transferring metal column itself to theupper plate member by the thermal conductivity of the heat transferringmetal column, it is possible to reduce the thermal resistance of theheat pipe. As the result, a heat sink having a small thermal resistancecan be obtained.

[0042] In addition, particularly in case that the generated heat densityof the heat generating part is high, there may occur a state where thereexists no working liquid in the evaporating part of the heat pipe,namely, what is called a dry-out phenomenon in which the working fluiddries out by the transferred heat. If the heat transferring metal columnis provided, as described above according to the heat sink of thepresent invention, since the heat generated from the heat generatingpart is transmitted in the vertical direction of the heat transferringmetal column through the lower plate member in such manner that the heattransferring metal column is uniformly heated as a whole by thetransferred heat, the generated heat density can be lowered along sidefaces (walls) of the heat transferring metal column. More specifically,the transferred heat is spread out along the side walls of the heattransferring metal column, thus lowering the generated heat density.According to the present invention, it is therefore possible tofabricate a heat sink including a heat pipe in which no dry-outphenomenon occurs.

[0043] In the example shown in this figure, the heat transferring metalcolumn 123 has nearly the same cross sectional area as that of the heatgenerating part 40, but the size is not limited to this. The heattransferring metal column 123 may be joined with the lower plate member21 or may be integrally formed as a unit with the lower plate member 21.In this case the heat of the heat generating part 40 is efficientlytransferred to the heat transferring metal column 123.

[0044] Moreover, in case that a wick is provided inside the heat pipe,the thermal resistance in the heat pipe may be reduced by cohering thewick and the heat transferring metal column to each other. A heattransfer mechanism in this case is as follows. The heat generated fromthe heat generating part is firstly transferred to the heat transferringmetal column through the lower plate member and then, transferred to thewick cohered closely to the heat transferring metal column, and then,transferred to the working fluid. In general, since porous or piledmeshed materials are used for a wick in order to enhance a capillaryoperation of the wick, the evaporation area may be further enlarged.

[0045] As a material for the heat transferring metal column, metalmaterial such as an aluminum or copper excellent in thermal conductivityis preferable, which is the same material as that of the heat pipecontainer, so as to be more adaptive to the working liquid. As describedabove, the heat transferring metal column is integrally formed as a unitwith the upper plate member. In this case the heat transferring metalcolumn and the lower plate member are joined with each other by means ofsuch a joining method as brazing, welding, soldering and the like. Theheat transferring metal column may be integrally formed as a unit withthe lower plate member. In this case the heat transferring metal columnand the upper plate member are joined with each other by means of such ajoining method as brazing, welding, soldering and the like.

[0046]FIG. 4 shows a heat sink of the present invention further providedwith a wick 50 comprising such as a mesh and the like inside a cavity 31along the interior surface of the container of the heat sink 1 shown inFIG. 1.

[0047]FIG. 5 is a plan view showing another embodiment of the upperplate member. The left half of FIG. 5 shows the inside of a cavity. Theright half of FIG. 5 shows the outside of the cavity. This upper platemember 13 has heat radiating fins 131, pressure resisting metal parts132 and a heat transferring metal column 133 all of which are integrallyformed as a unit with the upper plate member. Therefore, the thermalresistance between them is small. In the embodiment shown in FIG. 5, theheat radiating fins 131 comprise a plurality of portions arrangedintermittently in the shape of a swirl. In addition, in the same way thepressure resisting metal parts 132 comprise a plurality of portionsarranged intermittently in the shape of a swirl.

[0048]FIG. 6 is a plan view showing another embodiment of the upperplate member. The left half of FIG. 6 shows the inside of a cavity. Theright half of FIG. 6 shows the outside of the cavity. This upper platemember 14 has heat radiating fins 141, pressure resisting metal part 142and a heat transfer ring metal column 143 all of which are integrallyformed as a unit with the upper plate member. In this embodiment, theheat radiating fins 141 comprise a plurality of portions arranged in aradial manner with the heat transferring metal column 143 disposednearly as the center of the radial. In the same way, the pressureresisting parts 142 comprise a plurality of portions arranged in aradial manner with the heat transferring metal column 143 disposednearly as the center of the radial.

[0049]FIG. 7 shows an embodiment of a heat sink further provided with anelectrically driven fan. FIG. 7 is similar to the above-mentionedembodiments of a heat sink of the present invention in a feature that acavity 32 is formed by joining a lower plate member 23 and an upperplate member 15 to each other, and in a feature that a container 150,heat radiating fins 151 and a heat transferring metal column 153 areintegrally formed as a unit with the upper plate member 15.

[0050] The heat sink of FIG. 7 is further provided with an electricallydriven fan 6 being opposite to the heat radiating fins 151. In FIG. 7,the reference numeral 60 is a fan blade and the reference numeral 61 isa fan cabinet. An air current generated by rotation of the fan blade 60strikes the heat radiating fins 151 and the container 150 to moreforcefully prompt the discharge of heat. The heat radiating fins 151comprise a plurality of portions arranged in a radial manner similarlyto the example shown in FIG. 6. By doing so, a wind sent from theelectrically driven fan 6 comes to efficiently blow the heat radiatingfins 151.

[0051] As described above, a heat sink of the present invention shown inthe several embodiments has an advantage that it has a small number ofcomponents and is easy to make compact in size. And it is also excellentin cooling performance. In the present invention, the fins and the heatpipe do not necessarily need to be metallurgically joined with eachother but may be attached with each other thermally in one body throughgrease.

EXAMPLES Example 1

[0052] A heat sink provided with a cavity was formed by joining to eachother, by means of a brazing method, a lower plate member of aluminum of1 mm in thickness, 80 mm in width and 80 mm in length and an upper platemember 15 of aluminum of 38 mm in height, 80 mm in width and 80 mm inlength in which a heat transferring metal column, fins and pressureresisting metal part were integrally formed as a unit. A part of theupper plate member forming the side wall portion of the cavity was 5 mmin height. The heat transferring metal column was 25 mm in length, 25 mmin width and 4 mm in height, and was positioned in the middle part ofthe upper plate member. The fins comprised the portions arranged eachother in radial, each being 27 mm in width, 33 mm in height and 1 mm inthickness.

[0053] The upper plate member having the integrally formed heattransferring metal column, the fins and the pressure resisting metalpart as a unit was manufactured by casting aluminum. Moreover, a wickwas provided all over the inner walls of the cavity and the side facesof the heat transferring metal column.

[0054] Thus formed heat sink was attached to a CPU of 25 mm in lengthand 25 mm in width which is a heat generating part. The heat sink of thepresent invention efficiently cooled the CPU having a high amount ofgenerating heat of 70 W.

Example 2

[0055] A heat sink provided with a cavity was formed by joining to eachother, by means of a brazing method in the same way as described above,a lower plate member of aluminum of 1 mm in thickness, 80 mm in widthand 120 mm in length and an upper plate member 15 of aluminum of 30 mmin height, 80 mm in width and 120 mm in length in which a heattransferring metal column, fins and pressure resisting metal part wereintegrally formed as a unit. A part of the upper plate member formingthe side wall portion of the cavity was 6 mm in height. The heattransferring metal column was 20 mm in length, 15 mm in width and 5 mmin height, and was positioned in the middle part of the upper platemember. The fins comprised the portions arranged each other, each being80 mm in width, 24 mm in height and 0.8 mm in thickness. The upper platemember having the integrally formed heat transferring metal column, thefins and the pressure resisting metal part as a unit was manufactured bycasting aluminum.

[0056] Thus formed heat sink was attached to a chip which is a heatgenerating part. The heat sink of the invention efficiently cooled thechip having a high amount of generating heat of 100 W.

Example 3

[0057] A heat sink provided with a cavity was formed by joining to eachother, by means of a brazing method, a lower plate member of aluminum of0.6 mm in thickness, 100 mm in width and 100 mm in length and an upperplate member 15 of aluminum of 26 mm in thickness, 100 mm in width and100 mm in length in which a heat transferring metal column, fins andpressure resisting metal part were integrally formed as a unit. A partof the upper plate member forming the side wall portion of the cavitywas 4 mm in height. The fins comprised the portions arranged each other,each being 100 mm in width, 24 mm in height and 0.8 mm in thickness.Additionally, a wick was provided all over the inner walls of thecavity. The upper plate member having the integrally formed fins and thepressure resisting metal part as a unit was manufactured by castingaluminum.

[0058] Thus formed heat sink of the invention was attached to an MCMwhich was a heat generating part. The heat sink efficiently cooled theMCM which was a chip locally having a high amount of generating heat. Asis clear from the foregoing, according to the present invention, it ispossible to obtain a small-sized heat sink which is capable of coolingthe heat generating part with a high amount of generating heat and isexcellent in cooling performance.

[0059] As described above in detail, a heat sink of the presentinvention is of a small size and excellent in cooling performance.Furthermore, a heat sink of the present invention may cool a heatgenerating part with a high amount of generating heat.

What is claimed is:
 1. A heat sink comprising; (a) a plate-shaped heatpipe including an upper plate member and a lower plate member to form ahermetically sealed cavity, and a working fluid enclosed therein, and(b) at least one heat radiating fin integrally formed with said upperplate member on an outer surface of said upper plate member.
 2. A heatsink as claimed in claim 1 , wherein a heat transferring metal columnfor joining said upper plate member and said lower plate member witheach other in said cavity of said heat sink is integrally formed withsaid lower plate member on a portion corresponding to a heat absorbingportion of said plate-shaped heat pipe.
 3. A heat sink as claimed inclaim 2 , wherein a total area of side wall portion of said heattransferring metal column is larger than a sectional area of said heattransferring metal column.
 4. A heat sink as claimed in claim 1 ,wherein at least one pressure resisting metal column is integrallyformed with said upper plate member and/or said lower plate member insaid cavity of said heat sink.
 5. A heat sink as claimed in claim 4 ,wherein each of said heat radiating fin and said pressure resistingmetal part comprises at least two portions or a single portion, and saidat least two portions are intermittently arranged in a radial manner,whereas said single portion is continuously arranged in a radial manner.6. A heat sink as claimed in claim 4 , wherein each of said heatradiating fin and said pressure resisting metal part comprises at leasttwo portions or a single portion, and said at least two portions areintermittently arranged in a shape of a swirl, whereas said singleportion is continuously arranged in a shape of a swirl.
 7. A heat sinkas claimed in claim 5 , wherein a wick is disposed in said cavity ofsaid heat pipe.
 8. A heat sink as claimed in claim 6 , wherein a wick isdisposed in said cavity of said heat pipe.
 9. A heat sink as claimed inclaim 7 , wherein an electrically driven fan is disposed at a locationfacing said heat radiating fin.
 10. A heat sink according to claim 8 ,wherein an electrically driven fan is disposed at a location facing saidheat radiating fin.